Electrical control system



1366- 1942- J. T. VAUGHAN ELECTRICAL CONTROL SYSTEM Filed March 14, 1941 4 Sheets-Sheet 1 F/GZ RESISTANCE R .@N A H G M V Tl N H o J PERCERIQF TIME HIS ATTORNEYS Dec. 29, 1942. J. T. VAUGHAN ELECTRICAL CONTROL SYSTEM Filed March 14, 1941 4 Sheets-Sheet 2 8 .6 w 4 H s a f V VP I M d 6 4 M a lillllllrlllll m M n 4 4 m d O p. T O H.

m w w l w w F/GJ HIS ATTORNEYS Dec. 29, 1942. J. T. VAUGHAN 2,306,837

ELECTRICAL CONTROL SYSTEM Filed March 14, 1941 4 Sheets-Sheet 3 JOHN T} VAUGHAN BY yrm fl" HIS AT TOR NEYS Dec. 29, 1942. J, T VAUGHAN 2,306,837

ELECTRICAL CONTROL SYSTEM Filed March 14, 1941 4 Sheets-Sheet 4 INVENTOR JOHN T VAUGHAN HIS ATTORNEYS Patented Dec. 29, 1942 ELECTRICAL CONTROL SYSTEM John '1.

a: to The Electri I m any. of Ohio v han, Shaker Heights, om, assign. m o Controller is Manufactu- Olslo, a corporation Application March 14, 1941, Serial No. mass 11 Claims. (or. 112-208) This invention relates to a control system for an electric translating device, the illustrative examples hereinafter disclosed being improved control systems for automatically short circuiting the starting impedance in either direct current or alternating current motor circuits during acceleration of the motor and for introducing a time delay between the closing of successive starting switches, the extent of the time delay intervals being influenced by the load on the motor during acceleration. Embodiments of the invention in connection with other translating devices are apparent from the illustrative examples and are not specifically described.

Heretofore. in the control of translating devices by timing circuits, timing circuits similar to that hereinafter described have been provided. but the prior timing circuits either have been operatively connected to the translating devices in a manner such that the timing intervals thereof were inversely related to the magnitude of the particular electrical condition of the translating device on which the timing circuit depended for its energization, or were connected so that the timing intervals were directly related to the magnitude oi the particular electrical condition, in which case they were particularly adapted for use with alternating current motors or had other disadvantages and limitations.

Such prior timing circuits are set forth and described in United States Letters Patent No. 2,024,019, issued December 10, 1935, to David C. Wright, and in the copending patent application of William J. Kutcher and John D. Leitch, which issued as Patent No. 2,247,506 on July 1, 1941.

The timing circuit employed in the Wright patent is for a resistance welder and provides a time interval which is inversely related to the magnitude of the current flowing through the welding electrodes. A timing circuit similar to that or the Wright patent is employed in the Kutcher and Leitch application. but it is connected so as to provide timing intervals which are directly related to the amount of current flowing to an electric translating device and particularly to an alternating current device.

The timing control circuit of the present in- 'vention provides timing intervals which are directly related to the amount of current flowing to an electric translating device, as in the Kutcher and Leitch application, but is modified by the addition of certain elements and new cooperative relations of the component parts with each other and with the translating device, and consequently possesses numerous advantages over the timing control circuit therein disclosed. Among these advantages are a greater eilect on the time interval for a given change in current when used with direct current motors, greater adiustability of the time-current relation, a capability of operating under varying voltage relationships instead of r uiring a predetermined relationship of voltage values, forced acceleration-at all times, substantially a direct proportional relationship between the motor load and the extent of the time interval, and automatic reduction of the time intervals as the motor accelerates.

various other means have heretofore been used for automatically and successively short circuiting portions of an accelerating impedance in a motor circuit so that the starting current of the motor would not exceed certain predetermined values. Such of these systems as provide a dellnite time delay between the successive closing of the impedance shunting switches do not have the above advantages but instead certain disadvantages, in that, i: th time delay peri d, are adiusted for an intermediate load, the periods are too long for lighter loads and too short for heavier loads. As one example, a motor driving a definite mechanical load, such as a fan, accelerates at a rate which is dependent upon the frictional resistance as well as upon the total inertia of the load. The frictional resistance varies greatly with the temperature so that often during cold weather the acceleration contactors close too quickly if the acceleration time is deflnitely predetermined. As another example, a motor may be used to drive a wide range 01 loads varying from twice full load to extremely light loads, and, if the acceleration time is set so that excessive current peaks are prevented from occurring under heavy loads, then, on light loads. the motor is accelerated at a much lower rate than is economically or otherwise desirable.

In order to overcome such disadvantages in the case of direct current motors, numerous systems have been developed for automatically excluding starting resistance at a rate dependent upon the electrical condition of a motor circuit during the accelerating period. Two of the more common of such systems are known as counterelectromotive-force acceleration and current limit acceleration. One of the disadvantages common to both of these systems is that they cannot start or accelerate a stalled or too heavilyloaded motor since under such conditions the counter-electromotive force either does not exist or does not increase. In the case of current limit acceleration the current does not decrease sumciently to cause relay operation unless the motor rotates at an appreciable speed. Various means have been used to eliminate these defects, and such improved systems are known as combined time limit and current limit. All or such improved systems, however, are primarily adapted to determine only short time intervals, generally are not readily adjustable for different load conditions, require the use or an accelerating relay for each step of acceleration, or are incapable or 16) providing time delay intervals directly proportional to the motor load.

One or two minutes may be required to bring a motor driving a heavy inertia load up to full speed. This necessitates either the use of many 5 acceleration steps each having a relatively short time interval or the use of fewer steps each having a longer time interval. The use of fewer steps or longer duration is the more economical lated but in a substantially direct proportional relationship to the magnitude oi an electrical condition of the device.

Another important specific object is .to provide a system for controlling the operation of an electrical translating device by an operative relation between a condenser and an electrical condition of a circuit oi the device such that the charging rate of the condenser is directly proportional to the electrical condition.

An important object of the invention is to provide an improved system of motor acceleration in which a timing control circuit is provided which may be adjusted to provide a suitable acceleration oi the motor under normal working conditions, and which, without change of adjustment, controls more eflectively the acceleration of the motor under different or changing working conditions or under abnormal working condiof the two. but heretofore has not been used to as 29 tions.

great an extent as desired in the case of direct current motors because of the difiiculty of providing a satisfactory means to determine the long time intervals and still have the time intervals vary in close proportion to the motor load.

The present invention is an automatic motor control system for direct or alternating current motors which is capable of providing long time intervals between the successive operations of the accelerating switches and which time inter- 3o vals vary in close proportion to the motor load, thus permitting acceleration at a rate dependent upon the motor load during the accelerating period, and which is capable of causing the starting resistance to be shunted, even though the motor is stalled or the amount of motor current is excessive. The present system also is operative in a manner such that the duration of time which may be obtained between the successive opera-v tions of the accelerating switches is greater than 40 load, even though the motor inherently may require a long acceleration period. The present system also is particularly suitable for the acceleration of small direct current motors since the timing control circuit is much simpler and cheaper than those heretofore used to give timecurrent control of operation for that type of motor.

Its universality is further illustrated in some embodiments of the invention in which the time interval on each succeeding step is inherently shorter than on the preceding step as long as the motor is accelerating. This shortening of the time interval on successive steps of acceleration is desirable in the case of direct current motors driving a constant torque load where it is necessary that the peak currents during acceleration be kept nearly constant.

An important object of the present invention is to. provide a control system capable of providing the advantages above set forth.

A more specific object is to provide an improved system for controlling an electric translating device in accordance with the magnitude of a varying electrical condition oi a circuit of the device to be controlled.

Another object is to provide a timing control "circuit for an electrical translating device in Another object is to provide a control system for a direct current motor in which a means responsive to a predetermined potential is connected across an electrical energy absorbing device and capable of changing more effectively the condition of motor operation in relation to the load on the motor.

A correlative object of the present invention is to provide a system of direct current motor control which combines all of the advantages of the definite time delay systems and the current limit systems and which can be adjusted readily to provide a' wider range of acceleration periods than heretofore obtained.

Another object is to provide for a motor, a time-current control system which produces a greater effect on the acceleration time interval for a given change in motor current.

Another object is to provide an improved motorcontrol system incorporating a single timing control device which controls a plurality of accelerating switches in response to variations in the value of current in a motor circuit, the time delay intervals between operation of the switches 45 being longer when the current value is larger and being shorter when the current value is smaller.

Another object is to provide a direct current motor control system incorporating a single time delay device which controls a plurality of accelerating switches in response to variations in the value of current in a motor circuit and in which the successive time delay periods are progressively decrescent in extent.

Another object is to provide a readily adjustable time delay means for accomplishing the above objects, yet which has no moving parts other than the movable contacts of a small relay.

Other objects and advantages will become apparent from the following specification, wherein reference is made to the drawings, in which:

Fig. 1 is a simplified wiring diagram illustrating the timing control circuit of the present in- :(cntion, and connected with a direct current mo- Fig. 2 is a simplified wiring diagram illustrating a modified form of timing control circuit and connected with a direct current motor in the manner of Fig. 1;

Fig. 3 is a complete wiring diagram of'a direct current motor controller using the timing control circuit and connections of Fig. l, and con nected to a motor;

Fig. 4 is a complete wiring diagram of a direct current motor controller using the timing conwhich the time delay intervals are directly retrol circuit of Fig. 2, and connected to a motor;

s,soo,ea1 3 Fi 5 is a simplified wiring diagram illustrating the timing control circuit connected to an alternating current motor for controlling the same;

Fig. 6 is a fragmentary simplified wiring diagram illustrating the invention in connection with a modification of the controllers of Figs. 3 and 4;

Fig. 7 is a fragmentary simplified wiring diagram illustrating the invention in connection with another modification of the controllers of Figs. 3 and i;

I'ig. 8 is a graph showing exemplary relationships between the time interval and motor current obtainable by the present invention with different ratios of condenser capacity; and

Pig. 9 is a graph showingjhe effect of varying the timing resistor for different values of condenser capacity.

In the several figures, like parts are referred to by the same reference numerals.

For purposes of illustration, the invention is disclosed in detail in the drawings and description hereof as applied to a direct current motor of the series type and to an alternating current induction motor.

The invention in one form thereof comprises two condensers connected in series with each other and the combined condensers connected as a unit in parallel with the armature winding and series field winding of a direct current motor.

-When the motor is first connected to a power source through an accelerating resistance, the condensers charge immediately so that the total voltage drop across the armature and series field of the motor is divided between the condensers in inverse proportion to the capacities of the condensers. Concurrently, a circuit is completed from one terminal of the power source to the condensers through a timing resistor in a manner upon fiows through the operating winding of the control relay causing its operation. Operation of the control relay effects energization of the operating winding of an acceleration contactor which thereupon operates to short circuit a portion of the accelerating resistance. Concurrently, the

relay operation effects complete discharge of both condensers.

The voltage of the source applied to the control condenser during the time interval is reduced in relation to the magnitude of the voltage drop necessarily occurring across the starting resistance and the resultant is modified by the ratio of the condenser capacities, as more clearly disclosed by the mathematical analysis and structural description hereinafter set forth. The

time interval before the control condenser is charged to the breakdown voltage of the discharge device is directly related to the average magnitude of the voltage drop across the starting resistance during the time interval and, since the voltage drop across the starting resistance is inversely proportional to the counter-voltage of the motor, the time interval before breakdown of the discharge device is inversely related to the average magnitude of the counter-voltage. The

average magnitude of the counter-voltage during 75 the time interval is substantially inversely P oportionaltothemotorload,andconsequentlythe time interval is directly related to the motor load.

In another form of the invention, a control relay is operated directly by the charging current of the pair of series-connected condensers. When the charge on the control condenser approaches a predetermined value, the charging current has decreased to a predetermined value which permits the control relay to drop out. Drop-out of the control relay elects operation of an accelerating contactor to short circuit impedance in the motor circuit.

When either of the timing control circuits above described is used for controlling an alternating current motor, a potential transformer and rec,- tifier combination supplies a constant unidirectional voltage to the timing control circuit and a current transformer and rectfier combination sup- 2 0 plies a varying unidirectional voltage to the timing control circuit. The voltage supplied by the current transformer varies directly in accordance with the motor load and is thus operatively similar to the voltage drop across the starting resistance in the case of direct current motors, and the voltage supplied by the potential transformer is operatively similar to the voltage of the source in the case of direct current motors.

In Fig. l a direct current motor I I having an armature winding i0 and a series field winding i2 is arranged to be connected between the conductors 8 and '8 through the series connected acelerating resistors l4 and I6 when a switch 9 is closed. A condenser l8 and a condenser 24 are connected in series with each other and the combined condensers l8 and 24 are connected as a unit in parallel with the armature It and the minal of the condenser I8 is shown connected to the power circuit of the motor H at the junction point 2| between the series field i2 and the resistor l4, this connection could be made between the armature ill and the field i2 or at some other suitable place between the armature and a portion of the series connected accelerating resistance. The condensers may be fixed instead of adjustable.

A switch [9 is arranged to connect an adjustable resistor 22 between the conductor 8 and the interconnection between the condensers i8 and 24 at the junction point 23. The condenser 24 is shunted by a series connection including a gaseous discharge device 26 and an operating winding 28w of a relay 28. The discharge device 28, which may be of any suitable type but which preferably has cold electrodes in an attenuated atmosphere of neon, helium or the like,.

is shunted by a series connection including an adiustable resistor 38 and the normally-open contacts 28a of the relay 28. The contacts 28a are operable in response to the energization of the operating winding 28w. The relay 28 also has normally-open contacts 28b and 280 which may efiect control of the motor ii as hereinafter described in connection with Fig. 3. The discharge device 28 and the winding 28w might in some cases be preferably connected across the condenser or across both condensers as desired.

If the conductors 6 and 8 are connected to a suitable source of direct current (not shown) and the switches 9 and I 9 are closed simultaneously, current flows through the resistors ii and i4 and the motor ll,, causing a voltage drop across the motor H, which immediately charges the condensers Hand 24 so that the total voltage across the condensers l8 and 24 is equal to the voltage drop across the motor ii, the two condensers i8 and 24 dividing the total voltage in the inverse ratio of their capacities. Concurrently, a current starts to flow from the conductor 8 through the switch i9 and the resistor 22 to the junction point 23. The current divides at the junction point 23, part fiowing through the condenser i8 and the motor ii to the conductor 6 and part flowing through the condenser 24 to the conductor 6. As a result of the closure or the switch i9, the condenser 2t gradually increases its charge and the condenser it gradually decreases its charge to zero and then begins to increase its charge at opposite polarity.

With the connections as shown in Fig. l, the time interval required for the accumulated voltage across the condenser 2% to reach the discharge voltage of the device 26 is directly related to the magnitude of the average voltage drop across the starting resistors 54 and it during the time interval. However, if the condenser no and its connections were removed-and the condenser 24 left connected as shown in Fig. 1, the time required for the voltage across the condenser 24 to reach the dischargevoltage of the device 26 would be inversely related to the magnitude of the voltage between the conductors 6 and 9, would be constant if that voltage were constant, and would be unafiected by the electrical condition of the motor. If the terminal of the condenser it which is connected to the junction point 2i in Fig. 1 were connected directly to the conductor 6, the time interval would also be so related and constant and unafiected by the electrical condition of the motor. The addition of the condenser l8 if so connected in parallel with the condenser 24 would merely increase the total capacitance of the timing circuit so that the time delayinterval would be increased over the time interval obtainedwith the condenser 24 alone.

Assume, in the connections of Fig. 1, that closure of the switch 9 impresses the counter-voltage of the motor ii on the condensers l3 and 2d in a manner such that the right hand tel of the condenser l8 becomes negative and the left hand terminal of the condenser 26 becomes positive. Closure of the switch i9 impresses the voltage of the source less the voltage drop in the resistor 22 across the condenser 24 so that its left-hand terminal remains positive and current flows through the resistor 22 and the condenser 24 in such a direction as to increas the charge on the condenser 24. The voltage drop across the resistors i4 and I5 is now impressed across the circuit including the resistor 22 and the condenser l8. The polarity of the voltage drop across the resistors l4 and I6 is such as to cause current to flow through the condenser I! in a direction to decrease the charge on the condenser l8 with respect to its initial charge. The charge on the condenser I8 is consequently reduced at a rate dependent upon the value of the voltage drop across the resistors l4 and ld. After the charge on the condenser I8 reaches zero, the condenser l8 commences to charge at the opposite polarity and its right hand terminal becomes aaoaes? the condenser I l sheets the rate of charge or the condenser 24 so that a longer time is required before operation or the relay 28 than i! the condenser it were not present. The time required to charge the condenser 24 to the breakdown voltage or the device 28 is therefore a function 01' the voltage drop across the resistors i4 and is. Since the counter-voltage o! the motor II is inversely related to the voltage drop acrossthe resistors i4 and i8, the rate or discharge and recharge or the condenser I8 is dependent upon the counter-voltage and the time relay before operation of the relay 28 is therefore a function of the counter-voltage.

The operation 0! the circuit of Fig. 1 may be more clearly understood from the following mathematical analysis:

If go is the quantity of charge on the condenser it at any time t seconds after the switches 9 and 99 are closed, and or is the quantity of charge on the condenser 28 at any time t seconds after the switches 9 and it are closed, then the current through the resistor 22 is given by Because the condensers i8 and 24 are conon the condensers i8 and 24 must be equal. This may be expressed by the identity:

' i a; do

01 di 0, E (2) where Cr=the capacity oi the condenser l8, and Cz=the capacity of the condenser 24.

By Kirchofls law,

' Ri+v1=v= Ri+Vz=Vo where a =the resistance of theresistor 22 i =the current through the resistor 22,

Vo=the voltage between the conductors 6 and 8,

By substituting Equation 1 in Equations 3 and 4 the following relationships are obtained:

After integrating and solving Equations 5 and Q 6, the following equations are obtained:

Equation 8 may be written 1 v. V C V C "Czar-= From Equation 7 it is seen that an increase in the average voltage drop Va across the acceleratpositive. The rate or discharge and recharge or ing resistors l4 and I6 causes an increase in the time t required for the current i to decrease to a predetermined value alter the switch II is closed, other circuit values remaining constant.

The decrease in the current i is accompanied by a corresponding increase in the voltage across the condenser 24. Also. a decrease in the average value 01' the voltage drop V: causes a decrease in the time t for the current i to decrease to a predetermined value.

By altering the ratio of the capacities of the condensers i4 and 24 the degree 01' change in time for various values 01' the average voltage drop Vs can be adjusted over a wide range. This is illustrated by the curves of Fig. 8. In ,Fig. 8 the ordinate is the average voltage drop V: across the resistors i4 and I8, and the abscissa is the peroentage of time interval obtained, 100% time being considered as obtained when the average value of the voltage drop V3 is equal to 550 volts. The curve II indicates the range or time when the ratio of the capacity of the.condenser i8 to that of the condenser 24 is equal to 0.25, curve 52 indicates the range of time when this ratio is 0.375. and curve 53 is for a ratio of 0.5. d

The curves of Fig. 8 show that in the present invention there is substantially a straight line ratio between the time interval required to charge thecondenser 24 to the breakdown voltage of the discharge device 28 and the voltage drop V: across the starting resistors l4 and It. It the load on the motor ii is large. the amount of current through the resistors l4 and i8 islarge, the average value 0! the voltage drop V: is consequently large, and the time before operation of the relay 2| is longer than it the load were small. Since the average voltage drop Vs across the resistors l4 and I6 is directly proportional to the motor load. a suitable selection oi the ratio of condenser capacities results in the time intervals being directly proportional to the motor load. Since the motor load is inversely proportional to the counter-voltage oi the motor at any time during acceleration, the time intervals are inversely proportional to the average value of the countervoltage during the time interval.

It is obvious from the preceding discussion that even though the motor ii is stalled and does not accelerate, that the condenser 24 charges nevertheless and effects operation of the relay 2. after a time interval directly related to the current taken by the stalled motor. This feature makes possible so-called forced acceleration which is necessary in certain motor applications.

If the condenser I8 and its connections were not in the circuit of Fig. 1, the equation for the time required to charge the condenser 24 sufficiently for it to discharge through the device 2' is given by a v 8 RC: 10 Equation 10 may be written V t=RC, log, vulva Equation 9 may be written By comparing Equations 11 and 12 it is seen that the connection of the condenser I8 between the junction points 2i and 23 modifies the time interval directly with the average magnitude of the voltage drop V; across the starting resistors i4 and it during the time interval.

Further adjustability of the new timing control'circuit is illustrated by the graph 01 Fig. 9. In Fig.- 9 the abscissa is the value oi the resistance 22 in series with the switch I 8 and the ordinate is the time interval between closure or the switch I. and operation of the relay 28. The curve BI is obtained when the capacities of the condensers II and 24 are relatively small, curve 82 is obtained when the capacities are double those of curve 8!, and curve 83 isobtained when the capacities are three times those of curve Bl. Each of curves BI, 62 and 83 is for a particular average value 01' the voltage drop across the resistors i 4 and I6 and in each case the ratio of the capacity 01 the condenser I8 to that of the condenser 24 is 1 to 1.5.

It is a well-known fact that the average value of the voltage drop across the acceleration resistor in a direct current motor circuit during the interval between the first application of power and the occurrence of stable conditions or during the interval between the short circuiting of one section of the resistor and the occurrence of stable conditions is directly proportional to the load on the motor. Due to the fact that the curves H, 52, and 53 of Fig. 8 are substantially straight lines shows that the time delay obtained by the new timing control circuit is substantially directly proportional to the voltage drop across the accelerating resistor and consequently is substantially directly proportional to the motor load. The curves iii, 62 and 63 of Fig. 9 show that variations in condenser capacity once a definite ratio is selected do not affect this direct relationship and that the straight line ratio is obtained regardless of the adjustment of the resistor 22.

In Fig. 2 the relay 28 and the gaseous discharge device 26 of Fig. l are replaced by a relay 29 having normally-closed contacts 29a and an operating winding 29w. The winding 29w is connected in series with the resistor 22 between the resistor 22 and the Junction point 23. When the switches 9 and I! are first closed, the condenser charging current flowing from the conductor 8 through the resistor 22 causes immediate energization of the winding 29w and consequent operation of the relay 29. The relay 29 drops to its normal position when the charging current flowing through its winding 29w to the condensers i8 and 24 is reduced to a predetermined value due to change in potential on the condensers i8 and 24. The charging current through the winding 29w is inversely related to the potential across the condenser 24 and therefore the drop out of the relay 2915 controlled by the amount of charge on the condenser 24 as is the operation oi. the relay 28 of Fig. l.

The operation 0! the relay 29 is reversed from' that of the relay 28 and consequently to incorporate it in a motor control circuit requires that its contacts 29a be normally closed instead of normally open as is the case with the control contacts 28b and 280 of the relay 28.

In Fig. 3 the armature iii and the field l2 0! the motor II are arranged to be connected in series with the resistors l4 and i6 between the conductors 6 and 8 through the contacts 30a of an electro-responsive switch 30 having an operating winding 3010 and normally-open auxiliary contacts 30b. The energization of the winding 30w is controlled by a push button 32 having normally-open contacts 34 and normallyclosed contacts 36. One terminal of the condenser II is arranged 'to be connected to the Junction point 2|, between the series field winding i2 and the accelerating resistor it, through the contacts 42b of an electro-responsive relay 432 having an operating winding @220 and additional normally-open contacts @203 and normally-closed contacts 42a and $20. The other terminal oi the condenser I8 is connected through a resistor 2d of low ohmic value to one terminal of the condenser 24. The resistor 2e serves merely to limit the initial surge of the condenser charging current to protect the contacts filth. The other terminal of the condenser 26 is connected to a conductor i which is arranged to be connected to the conductor 6 through the contacts 3% of the switch 30 or through the contacts 36 of the push button 32. The series connected discharge device as and the relay winding 28w are connected across the terminals of the condenser 26 from the conductor 7 to the junction point 25. The adjustable resistor 38 is connected in series with the contacts 28a across the discharge device 26 to form a discharge circuit for the condenser 28 through the winding 28w and consequently a tern porary holding circuit for the relay 28. The nor- ,maily-closed contacts 32m of the relay it compiete another discharge circuit for the condenser 2 3 through an adjustable resistor 39. The normally-closed contacts 62c complete a discharge circuit for the condenser 58 through the resistor 2a. The normally-open contacts @211, when closed, connect the junction point 23, between the condenser 2d and the resistor 28, to the conductor 8 through a fixed resistor i7 and the adjustable resistor 22. The winding iZw of the relay 412 is arranged to be energized concurrently with the winding 30w of the switch so, being connected between the conductors i and 8 through the normally closed contacts 600 of an electro-responsive relay 0 and the normally closed contacts 440 of an electro-responsive switch 44.

The accelerating resistor i6 is arranged to be short circuited by an electro-responsive switch $6 and the switch 44 is arranged to short circuit both of the accelerating resistors i4 and it. The

switch 44 has an operating winding w, normally-open contacts 34a and Mb and normallyclosed contacts Md in addition to the normallyolosed contacts 4 30. The switch 46 has an operating window @620, normally-open contacts @186,

asoassv from the conductor 8 to the conductor 1 and the closure of the contacts 301 maintainsthis circuit. The energizing circuit for the winding w is iron: the conductor 8 through the contacts 38 and the winding Sew to the conductor 8. The energizing circuit for the winding to of the relay 32 is from the conductor 1 through the normany-closed contacts Mo and 6c and the winding 62w to the conductor 8. I

The relay 32 operates in response to the energization of its winding 52w to open its contacts (32a and 520 to interrupt the discharge circuits for the condensers 26 and i8, respectively, to close its contacts 622; to connect one terminal of the condenser it to the junction point 2!, and to close its contacts 3203 to connect the junction point 23 to the conductor 8 through the resistors iii and 22. As a result of the closure of the contacts 41% and the interruption of the condenser discharge circuits, the condensers i8 and 26 immediately charge collectively to a voltage equal to the voltage drop across the motor Ii, dividing the charge in the inverse ratio of their capacities.

Closure of the contacts 62d starts a gradual increase of the charge on the condenser 2 3 and a gradual decrease of the charge on the condenser id in the manner described in connection with Fig. 1. One circuit to the condenser 24 is from the conductor 7, through the condenser 24, the junction point 23, the contacts 32d, and the resistors ii and 22 to the conductor 8, and another is from the junction point 23 through the condenser ie to the Junction point 2!. When the voltage across the condenser 2% reaches a value equal to the breakdown voltage of the discharge device 28, the device 2d becomes conducting and the winding 2610 is energized by the discharge current from the condenser 24 causing the relay 28 to operate and close its contacts 28a; 28b, and 280. Closure of the contacts 28a of the relay 28 completes a further discharge circuit for the condenser 2 through the resistor 38 and the winding 28w, and closure of the contacts 28b. completes an energizing circuit for the winding to through the normally-closed contacts 46b of the switch 46. Due to the presence of the resistor 38, the discharge current of the condenser and 46d and normally-closed contacts 68b. 60

The contacts 8612 when closed complete a shunt circuit around the resistor i6 and the contacts 4 301 when closed complete a shunt circuit around both of the resistors and it.

The relay 28, the operating winding 2810 of which is in a discharge circuit of the condenser 24, has normally-open contacts 28a, 28b and 280. The relay 49 has an operating winding flilw, normally-open contacts 60a and 40d, and normallyclosed contacts 80b in addition to the normallyclosed contacts 400.

A more thorough understanding of the controller of Fig. 3 may be had from the following description of its operation. Assuming that the conductors e and 8 are connected to a suitable source of direct current (not shown), closure of the contacts 35 of the push button 32 efiects concurrent energizations of the windings 3010 and 42w. The contacts 3011 close in response to energization of the winding 30m to connect the motor I I between the conductors 6 and 8 through the resistors M and I6. The contacts 30b of the switch 30 close to form a holding circuit for the winding 3010 through the stop contacts 36 independent of the opening of the contacts 34. C10- sure of the contacts 34 also completes a circuit it is limited and thus the winding 28w remains energized for a brief interval.

As a result of the energization of its winding tow, the relay it operates to close its contacts 40a and 40d and to open its contacts 40b and Me. Closure of the contacts Illa completes a holding circuit for the winding 40w around the contacts deb. Opening of the contacts 40b prevents the completion of a circuit to the winding w through the contacts 48c, and opening of the contacts the causes deenergization of the winding 4220 of the relay 2. Closure of the contacts 40d causes energization of the winding |6w of the switch 48 through the normally-closed contacts 44d of the switch 44. 1

As a result of the energization of the winding 46w, the switch 46 operates to close its contacts 460, 46c, and 46d and to open its contacts 46b. Closure of the contacts a completes a shunt circuit around the accelerating resistor l8 resulting in an increase in the current flowing to the motor H and consequently resulting in an increased motor torque. The time interval between the olosure of the contacts 30a 01' the switch 30 and the closure of the contacts 46a of the switch 48 is therefore measured by the timenergized by virtue oi the closure oi the contacts- 44a. Closure oi the contacts 44c oompletes a circuit to the winding 4410, but this circuit is interrupted by the now open contacts 44b.

As a result oi the deenergisation oi the winding 4210 by opening oi thecontacta 44c, the contacts 42d and 420 oi the relay 4: close-to complete the discharge circuits ior the condensers I4 and II, respectively, through the resistors II and 24, respectively, and the contacts 41d and 42b open to disconnect the condensers II and 14 from the conductor I and the junction point 2i, respectiv lv.

The winding 2410 is deenergized aiter a time interval depending upon the length oi time re- 1 quired for the condenser 24 to lose its charge.

This time interval need only be long enough ior the switch 44 to operate. The relay is then returns to its normal position and opens its contacts Ilb causing deenergization oi the winding 4410 and opens its contacts ac to interrupt one circuit to the winding 44w, but the winding 44w remains energized through the normally-closed contacts 44d and the now closed contacts 44d.

Deenergization oi the winding 44w Permits the relay 40 to return to its normal position, and thereby to close its contacts 44c to again complete an energizing circuit ior the winding 42w oi the relay 4: through the contacts 44c. Opening oi the contacts 40d interrupts another circuit to the winding 4410 but the winding 44w remains energized through the contacts 44d and 44d.

Upon energization oi the winding 4210, the relay 42 again operates to remove the short circuit connections from the condensers II and 24 and to connect them ior charging in the same manner as beiore. After a time delay interval, depending upon the average voltage drop across the resistor l4, the discharge device 24 again breaks down to cause energization oi the winding Ilw and consequent operation oi the relay 2:. Closure oi the contacts 24b completes an ener- I spectively.

gizing circuit for the winding 44w oi the switch 44 through the normally-closed contacts 44b and through the now closed contacts 0. The relay 4| does not operate at this time because the circuit to its winding is interrupted by the now open contacts 44b. Closure oi the contacts 24a completes the discharge circuit ior the condenser 24 through the resistor is, and closure oi the contacts 24c completes an energizing circuit ior the winding 44w which is independent oi the contacts 44d.

As a result oi the energization oi its winding 4410, the switch 44 operates to close its contacts 44a and 44b and to open its contacts 44c and 44d. Closure oi the contacts 444 short circuits the resistors l4 and it to connect the motor ii directly across the supply conductors 4 and 4. Closure of the contacts 441: completes a holding circuit for the winding 44w directly across the conductors I and 0. Opening oi the contacts 44c deenergizes the winding 4210, and opening oi the contacts 44d discontinues one circuit to the winding 44w. when the condenser 24 is discharged, the

The timing control circuit including the condensers 24 and I! has provided a time interval between the operation of the switch 38 and the switch 44 and a further time interval between the operation oi the switch 46 and the switch 44, each oi which time intervals is directly dependent upon the average voltage drop across the accelerating resistance during the duration oi the interval and is therefore directly related in extent upon the magnitude oi the motor load. Since, ior any given load on the motor ii, the voltage drop across the resistor l4 after operation of the switch 48 is less than the voltage drop across both resistors l4 and I6 beiore the switch 44 operates provided that the motor is accelerating, the time delay interval between the operation oi the switches 44 and 44 is less than the time delay interval between the operation oi the switches 30 and 46. That is, the successive time delay intervals for the same motor load are decrescent in extent as long as the motor is accelerating.

Ii at any time during the operation of the motor II it is desired to stop it, the push button I2 may be operated to open its contacts 36 resulting in deenergization oi the winding 30w. The switch 30 consequently opens its contacts Ila to disconnect the motor ii from the conductor 4 and opens its contacts 30b to interrupt the connection between the conductor 6 and the conductor 1 and thereby eilects deenergization of any oi the operating windings 4410, 4210, 4410, and 4610 which may be energized. Deenergization oi the relay 4210 causes closure of the contacts 420 and 420 to effect complete discharge oi the condensers 24 and I8, respectively, so that when the motor I I is again restarted initial conditions are such as to give normal timing.

A direct current motor controller similar to that oi Fig. 3 but employing the series connectcd relay 2O oi Fig. 2 is shown in Fig. 4. The controller oi Fig. 4 utilizes an electro-responslve switch 41 having one more pair of normallyopen contacts than the corresponding switch 48 oi Fig. 3 and an electro-responsive switch 45 having one less pair oi normally-closed contacts than the corresponding switch 44 of Fig. 3.

A condenser 4i is connected in parallel with the winding 40w oi the relay 40 and a. resistor 43 is connected in series with the winding 40w so that operation of the relay 40 is retarded upon energization of the winding 40w but any other suitable retardation means for the relay 44 may be used. In other'respects the control elements oi Fig. 4 are similar to those oi Fig. 3, and any diiierences in their operation is fully explained in the following description of operation of the complete controller of Fig. 4.

Upon closure of the start contacts 34 of the push button 42 oi Fig. 4, a circuit is completed from the conductor 6 through the winding 30w oi the switch 30 to the. conductor 8 and from the conductor 4 to the conductor 1. Assuming winding 1410 is deenergized and the conseq en is that the conductors t and I are connected to a suitable source of direct current (not shown), the switch 8!! operates in response to energization of its winding 30w to close its contacts 38a and 30b. Closure of the contacts 39a connects the motor it between the conductors and 8 in series with the resistors It and i6. Closure of the contacts 30b completes a holding circuit for the winding 30w around the start contacts at and through the stop contacts 36 of the push button 32. The conductor 7 is connected to the conductor 6 through the contacts 381).

Concurrently with the energization of the winding 3820, the winding 612w of the relay 62 is energized over a circuit extending from the now energized conductor 1 through the normally closed contacts 60c and 350 to the conductor 8. Energization of the winding (3220 causes the relay 432 to open its contacts 62c and 62a and to close its contacts 42b and 32d. Opening of the contacts 62a and Q20 interrupts the discharge circuits for the condensers 2d and 68, respectively, through the resistors 38 and 28, respectively. The contacts Zb when closed connect the condensers i8 and 2t and the resistor 2t? of low ohmic value across the motor ii in series with each other. As a result, the condensers i8 and 2d charge immediately to a total voltage equal to the voltage drop across the motor H, dividing the charge in the inverse ratio of their capacities. Closure of the contacts 62d connects the junction point 23 to the conductor t through the winding 29w of the relay 29 and the resistors l7 and 22. A condenser charging current immediately flows through the winding 29w causing operation of the relay 29 and a gradual increase in charge on the condenser 26. Concurrently, the condenser it begins to lose its charge. The charging rate of the condenser 24 is dependent upon the voltage drop across the resistors Hi and it due to the circuit relationships previously described, and after a lapse of time depending upon the average value of the voltage drop across the resistors id and IS, the current through the winding 2910 is reduced to a value such as to permit the relay 29 to drop out.

The condenser M and the'resistor 48 so delay the operation of the relay 40 that it does not have time to operate when the push button contacts 3d are closed before the contacts 29:: of the relay 29 open. Drop-out of the relay 29 due to a decrease in the condenser charging circuit causes reclosure of the contacts 29a. Closure of the contacts 29a completes a circuit to the winding 40w through the normally-closed contacts 47b of the switch 67. In response to the energization of its winding 6010, the relay ill operates to close its contacts 50a and 50d and to open its contacts 46?) and Mic.

The opening of the contacts $00 causes deen- I ergization of the winding 52w of the relay &2 which thereupon operatesv to open its contacts 42b and 42d to interrupt the condenser charging circuits and to close its contacts 42a and 420 to complete the discharge circuits for the condensers 24 and i8 respectively.

Closure of the contacts 40d completes an energizing circuit to the winding 87w of the switch N from the conductor 7 to the conductor 8. Opening of the contacts 40b prevents energizetion of the winding 4510 upon closure of the contacts 41c. Closure of the contacts 40a completes a holding circuit for the winding 4020 which is independent of the contacts d'ib.

In response to energization of its operating aaoaesc winding 41w, the switch 4i operates to close its contacts Ma, 41c, 51d, and Me and to open its contacts 41b. Closure of the contacts ila completes a shunt circuit around the accelerating resistor IE to cause an increase in the current flowing to the motor it and consequently an increase in motor torque. Closure of the contacts ile does not complete a circuit at this time due to the fact that the contacts 40b are open. Closure of the contacts -iid completes an energizing circuit for the winding 62w of the relay 52 through the normally-closed contacts 350 of the switch 55 which is independent of the contacts (lilo oi the relay it. Closure of the contacts file completes a holding circuit for the winding llw directly across the conductors l and 8 which is independent of the contacts and.

The relay (12 operates in response to energizetion of its winding 62w to interrupt the discharge circuits for condensers 2d and it! by opening its contacts lZa and 620, respectively, and to close its contacts 621) and 62d. The winding 29w of the relay 29 is again energized by the'condenser charging current upon closure of the contacts ll2b and 52d. Energization of the winding 29w causes the relay 29 to open its contacts 29a causing deenergization of the operating winding lllw. Reclosure of the contacts 50b as a result of deenergization of the winding 40w does not complete a circuit to the winding 55w at this time because the contacts 29a are open. Closure of the contacts etc does not effect any circuit changes at this time because the contacts did in parallel therewith are closed and, likewise, opening of the contacts (ltd has no operative effect because the contacts Me in parallel therewith are closed. 7

After a time interval directly dependent upon the load on the motor H, the relay 29 is deenergized and again closes its contacts 29a. Closure of the contacts 29a completes an energizing circuit for the winding 4510 through the normally-closed contacts 80b and the now closed contacts We. The switch 45 thereupon operates and as a result closes its contacts 45a and 45b and opens its contacts 450. Closure of the contacts 45a shunts the resistor It to connect the motor it directly across the conductors 6 and 8. Closure of the contacts 45b completes a holding circuit for the winding 45w directly across the conductors l and 8. Opening of the contacts Q50 deenergizes the winding 42w causing the relay #52 to again complete through the contacts 62a and $20 the discharge circuits for the condensers 24 and I8, respectively.

Opening of the contacts 36 of the push button at any time during operation of the motor I i discontinues the energization of the winding 3010,

age voltage drop across the resistor M on the second step if the motor is accelerating. As a result, in controllers having two or more steps of acceleration, the time interval of each succeeding step is shorter than that of the preceding step as long as the motor is accelerating. Shortening of the time interval of successive steps oi acceleration is desirable in the acceleration oi direct current motors driving a constant torque load it the peak currents during acceleration must be kept substantially constant.

In cases where this foreshortening oi the acceleration steps is not desired, the circuit 01' Fig. 6 or of Fig. 7 may be incorporated in the controllers of Figs. 3 and 4. In Fig. 6 an adjustable resistor 49 is provided which may be connected between the contacts 42b and the junction point 2! when the contacts 48 are open and the contacts 48g are closed. When the connection oi Fig. 6 is employed in either of the controllers of Figs. 3 or 4, the first timing interval begins when a circuit is completed from the condenser i8 to the junction point 2| through the contacts 42!) of the relay 42 and the normally-closed contacts 48). The contacts 48 may be normally-closed auxiliary contacts on either the switch 46 or 41 of Figs. 3 or 4. The contacts 489 may be normally-open contacts on either the switch 45 or 41. The second timing interval begins after the switches 46 or 41 have operated so that the contacts 48! are open and the contacts 48 are closed. The voltage drop across the resistor 49 which is connected in series between the condenser l8 and the junction point 2| when the contacts 48g are closed, causes a smaller condenser charging current to fiow in the circuit including the condenser i8 and the timing interval on the second step therefore can be made as long or longer than the first timing interval by adjusting the value of the resistor 49.

If the circuit of Fig. 7 is included in the controller of Figs. 3 .or 4, a like operation to that obtained by the use of the connection of Fig. 6 is accomplished by automatically varying the adjustment of the timing resistor 22 by the auxiliary contacts 48! and 48 in an obvious manner.

In Fig. 5 is illustrated one way in which the timing control circuit of this invention may be connected for controlling an alternating current motor. An alternating current motor 11 is arranged to be connected to a source oi three phase power indicated by the conductors L1, L2, and La by means or an electro-responsive switch 10 through the conductors 85, 51, and 69. Interposed in the conductors 65, 81 and 69 are accelcrating impedances ll, 13, and 15, respectively. An electro-responsive switch 14 is arranged to have its main contacts short circuit the impedances 'll, 18 and 15 when its operating winding "to is energized. The switch 14 has normallyopen auxiliary contacts 14a and normally-closed auxiliary contacts 14b, and the switch I0 has an operating winding 18w and normally-open auxiliary contacts 10a. 1

The motor 11 is illustrated as a squirrel cage induction motor having accelerating impedance in its primarycircuit, but applications of the timing controlcircuit to other types of alternating current motors controlled by varying either primary or secondary impedance is obvious from Fig. 5 and are not specifically described.

The switch 10 corresponds to the switch 30 of Figs. 3 and 4 and its winding 18w is arranged to be energized from the contactors L2 and La when the contacts 84 of the push button 32 are closed. Energization of the winding 'lliw eiIects closure of the main contacts of the switch 18 to energize the conductors 85, 61, and 69 and effects closure of the auxiliary contacts Ilia to complete a holding circuit for the winding 10w through the normally-closed contacts 38 of the push button 32. Closure of the contacts 84 or the contacts 18a also partially completes a circuit from the con ductor Is, through the conductor 12, the normalLv-open contacts 28b oi! the relay 28, and the winding 14w to the conductor 61, but this latter circuit is interrupted by the normally-open contacts 28b of the relay 28. The timing control circult 01' Fig. 1 including the relay 28 is shown in Fig. 5, but the modified timing control circuit of Fig. 2 can be employed as well and its cooperation with an alternating current motor is apparent from the description of Fig. 5.

A constant unidirectional voltage, corresponding to the voltage of the source in the case of direct current motor control, is applied to the timing control circuit and is obtained from a potential transformer 90 having its primary winding 9| connected across the conductors 61 and 69 through the normally-closed contacts 14b and its secondary winding 92 connected to a full wave rectifier circuit 93 including the rectifying device 93a and the filter condenser 94. The output or the secondary winding 92 of the transformer 98 is rectified by the rectifier circuit 93 in the usual manner and the rectified output voltage of the transformer 90 is applied across a resistor 95 with the polarity as indicated. A circuit is completed from the positive terminal 91 of the resistor '95 through a conductor 96, the adjustable resistor 22, the junction point 23, and the condenser. 24 to the negative terminal 98 of the resistor 85. If this connection alone were present the condenser 24 would charge, after closure of the switch 10, in a predetermined interval of time depending upon the potential between the conductors 81 and 69, and upon reaching a predetermined charge would discharge through the discharge device 26 and relay winding 28w to operate the relay 28, which would effect operation of the switch 14. As long as the voltage between the conductors 61 and 69 remained constant, this time interval would also be constant, and no time current effect would occur.

To cause the time interval to vary indirect relationship to the load on the motor 11, a current transformer having its primary winding 8| connected in series with the conductor 69 and its secondary winding 82 connected to a full-wave rectifier circuit 83 including the rectifying device 83a and the filter condenser 84 is provided. The output of the transformer 80 is rectified by the rectifier circuit 83 in the usual manner, and the rectified output of the transformer 80 is supplied to a resistor 85 with polarities as indicated. The negative terminal 88 of the resistor 85 is connected to one terminal of the condenser l8 and the positive terminal 81 of the resistor 85 is connected to the conductor 96. The other terminal of the condenser I8 is connected through the junction point 23 to one terminal of the condenser 24 as in Fig. 1.

Since the amount of current flowing to the motor I1 is directly related to the motor load, and since the unidirectional voltage output of the rectifier circuit 83 is directly proportional to the motor current, the voltage across the resistor 85 corresponds to the voltage drop across the resistors l4 and 16 in the case of the direct current motor of Fig. 1.- The voltage drop across the resistor and. the voltage drop across the resistor 85 respectively are applied to the condensers i8 and 24 in the same manner as the voltage of the source and the voltage drop across the resistors i4 and I8 in Fig. 1, except that in Fig. 5 the condensers i8 and. 24 do not receive the small initial charge. As a result the time required for the coandenser 24 of Fig. 5 to reach a predetermined charge is directly proportional to the amount of current flowing to the motor and to the load on the motor as is the case in Fig. 1.

Upon expiration of the time delay interval required to charge the condenser 24, the condenser 24 discharges through the device 26 and the winding 28w causing operation of the relay 28 and consequent closure of the contacts 28a and 28b. Closure of the contacts 28b completes the previously traced circuit to the winding 14w and as a result of the energization of the winding 14w, the switch 14 operates to short circuit the impedances ll, 13, and 15, to close its auxiliary contacts Ma, and to open its auxiliary contacts 742). Current from the source L1 and L2 and La may now flow directly to the motor ll undiminished by accelerating impedance. The closure of the auxiliary contacts 14a completes an obvious holding circuit for the winding 14w independent of the opening of the contacts 28b. The contacts 28b open as soon as the discharge current of the condenser 24 flowing through the winding 28w, the contacts 28a, and the adjustable resistor 38 has decreased to the drop out value of the relay 28. 1

Opening of the auxiliary contacts 14b disconnects the primary winding 9| from the conductors 69' so that the timing control circuit remains unenergized during normal operation of the motor I1.

I claim:

,'1. A motor and control system combination, comprising a direct current motor. an accelerating resistor connected in series therewith, a pair of condensers connected in series with each other and across the motor armature, whereby the condensers are collectively charged to a voltage equal to the voltage drop across the motor in inverse proportion to their respective capacities when the motor and accelerating resistor are connected across a source of power, an electrical connection between the common terminal of the condensers and a point on the accelerating resistor which is remote from the common terminal of the motor and accelerating resistor, a timing resistor interposed in said connection, whereby upon operation of the motor one condenser begins to increase its charge and the other condenser begins to decrease its charge at rates dependent upon the electrical condition of the motor, and means operable in response to an accumulated charge on at least one'oi said condensers for controlling the motor.

2. A control system for controlling the control means of the knowncombination of an alternating current motor and control means for the motor, said system comprising a current responsive means adapted to produce a unidirectional voltage directly related to the amount of current flowing to the motor, means adapted to produce a substantially constant unidirectional voltage, a potential absorbing device, electrical connections between a portion of said device and said constant voltage producing means for subjecting said portion of said device to said substantially constant unidirectional voltage, electrical connections between another portion of said device and said current responsive means for simultaneously subjecting said last named portion of said device to said varying unidirectional voltage, a timing resistor included in said connections, said portions of said device being connected in series with each other, whereby when charges are produced by said voltages on the portions, respectively, the

rates of accumulation of potential by the portions are mutually afiected in a manner such that the time required to accumulate "a made-- termined potential on at least one of said portions of the device is directly related to the sum of said voltages, and means rendered operative in response to the accumulation of said predetermined potential for controlling the control means.

3. A motor and control system combination, comprising an electric motor, an accelerating resistor, means connecting said motor and said resistor in series across a source of direct current power, a pair of condensers connected in series with each other across the motor armature, means responsive to a predetermined potential across at least one of said condensers for controlling the current flowing to said motor, a resistance means, and means electrically connecting one of said condensers across said source in series with said resitsance means, whereby said condensers are subject to a charging potential dependent upon the counter-electro-motive force of the motor when the motor is rotating and to a substantially constant potential when the motor is not rotating.

4. The combination with a motor and control system comprising a direct current motor and an accelerating resistance connected in series, means adapted to connect said series connection across a source of power, shunting means including a capacitive time delay device operative when the device is charged to a predetermined .value to shunt a portion of the accelerating resistance while the motor is accelerating, whereby the voltage drop across said resistance is reduced, and thereafter to shunt successively and cumulatively additional portions of said accelerating resistance, of a second capacitive device operatively associating the first capacitive device with said resistance to cause said first capacitive device to charge at a rate inversely proportional to the. voltage drop across said resistance, whereby said shunting operations take place after time intervals respectively, each of which intervals is substantially directly proportional in extent to the average value of the voltage drop across the resistance throughout its own duration.

5. A motor and control system combination, comprising a direct current motor, an accelerating impedance, switch means operable to vary the efiective value of said impedance in steps,

and timing means operable after time delay intervals substantially directly proportional to the current flowing to the motor during the respective intervals for causing operation of said switch means after each interval, said timing means being responsive to the change in value of said impedance upon successive operations of said switch means'for causing successive time delay intervals to be decrescent in extent.

6. In a motor acceleration system wherein a capacitive charge absorbing device operates as an arresting means to arrest the action of an accelerating control means for a predetermined period and is connected in series with a timing resistor to a source of substantially constant voltage for charging thereby and wherein said accelerating control means is arranged to control the eflective resistance of an accelerating resistor connected in series with a direct current motor, the combination with said charge absorbing device of a second capacitive charge absorbing device electrically interconnecting the common terminal of said first charge absorbing device and said timing resistor with the common terminal of said motor and said accelerating resistor, whereby the charging time oi the first charge absorbing device is modified so as to depend upon the ratio of the electrostatic capacities oi the two charge absorbing devices, the electrical condition of the motor during the charging interval, and the magnitude of-the substantially constant voltage.

7. The combination with a motor and a control system combination, comprising a direct current motor, a condenser means, electrical connections between the condenser means and said motor operable for charging the condenser means at a rate inversely related to the load on the motor, whereby the charging current of the condenser means decreases to a predetermined value in a time interval directly related in extent to the load on the motor, of means responsive to said predetermined value of the charging current of the condenser means for changing th condition 01' motor operation.

8. A motor and control system combination, comprising a direct current motor, an accelerating resistor connected in series therewith, a pair oi series connected condensers, a timing resistor having one of its terminals connected to the common terminal of the condensers, means connecting the other terminals of the said condensers, re spectively, to two of the motor terminals across which the voltage changes are related to changes in voltage in the motor armature for subjecting the condensers to the countervoltage of the motor, and means connecting the other terminal of the timing resistor to the accelerating resistor at a point remote from the point oi connection of the I accelerating resistor and the motor.

9. A controller for an electrical translating device, comprising a pair of condensers and a resistor connected in Y with respect to each other,

- means adapted to connect the outside terminals cumulate charges, respectively, at rates which are interdependent, and means responsive to the accumulated charge on at least one of said condensers for controlling said translating device.

10. A controller in accordance with claim 9 characterized further in that the capacities of the condensers are so related that the rate of charge accumulation on at least one of said condensers is inversely proportional to the magnitude oi the variable voltage.

l1. A motor and control system combination, comprising a direct current motor, an accelerating resistor connected in series therewith, switch means operable to vary the eflective value oi said resistor in steps, timing means, operative during rotation and non-rotation of the motor and after each of successive time delay intervals of which each is substantially directly proportional to the average voltage drop across said resistor throughout its own duration for causing operation of said switch means after each interval, and said timing means being responsive to the change in value of said resistor caused by operation of said switch means to cause said successive time delay intervals to be decrescent in extent.

12. A motor and control system combination.

nil

comprising a direct current motor, an accelerating resistor connected in series therewith, shunting means operable for shunting at least a portion of said resistor, means operatively associated with said shunting means for causing said shunting operation to take place after a time delay interval substantially directly proportional to the amount of current flowing to the motor during said interval when the motor is connected to a source of power, and said means including a capacitance electrically associated with said resistor and having a linear relationship between its charging time and the magnitude of the voltage drop across said resistor.

13. The combination with a plurality oi successively operable electromagnetic accelerating switches for an electric motor, a condenser, a timing resistance, and connecting means for connecting said condenser and said timing resistance in series across a-voltage source of a second condenser having one terminal connected to the common terminal of said first condenser and said timing resistance, additional connecting means for connecting the other terminal of the second condenser and the other terminal of said timing resistance to a voltage source, and means responsive to the electrical condition 01 at least one of said condensers for eilecting operation of said switches after time delay intervals, whereby, when the first connecting means is connected across a source of substantially constant voltage and the additional connecting means is connected across a source of variable voltage having an average magnitude directly related to an electrical condition of the motor, said time delay intervals are directly related to the magnitude of the variable voltage or the electrical condition of the motor.

14. A combination in accordance with claim.

16. A motor and control system combination,

comprising a direct current motor, an accelerating resistance connected in series with said motor, switch means operable to vary the effective value of said resistance, a capacitive time delay means having a time delay period directly proportional to the average magnitude of a voltage applied across two oi its terminals during said period, means connecting said two terminals of the time delay means across at least a portion of the accelerating resistance, said time delay means including means for eilecting operation of said switching means at the expiration of said time delay period.

17. Apparatus for controlling the operation oi an electric translating device, a pair 01' condensers and a resistor connected in Y with respect to each other, means connecting the outside terminals oi one condenser and oi the resistor across a source of substantially constant voltage, means connecting the outside terminals of the second condenser and of the resistor across a source of variable voltage which varies in magnitude in accordance with the electrical condition of the device to be controlled, whereby, when the Y- connected condensers and resistor are connected across said voltage sources, the voltage across each of said condensers increases toward a predetermined voltage, and means responsive to the attainment of said predetermined voltage by at least one of said condensers for controlling said device, the ratios of the capacities of said condensers to each other and of the magnitude of said predetermined voltage to the magnitude of said constant voltage being such as to cause the time for the said one condenser to reach said predetermined voltage to be substantially directly proportional to the magnitude of said variable voltage.

- JOHN T. VAUGHAN. 

